When the air is very hot in the passenger compartment of a stationary vehicle, an air conditioner reduces it to a more acceptable temperature before the occupants of the vehicle take their places, as disclosed for example in FR-A-2 690 387.
In a known device of this type, notably for a vehicle with a thermal engine, the compressor is driven by a special electric motor both when the main engine is working and when the vehicle is parked. This electric motor has a relatively high energy consumption. Moreover, when parked, the device is fed by the on-board battery of the vehicle. If the device is used for a long time under these conditions, the battery runs the risk of being discharged to the point of no longer allowing the starting up of the thermal engine.